The present invention relates to robotic tool changers, and more particularly to a robotic tool changer for transferring secondary current across the tool changer.
Industrial robots have become an indispensable part of modern manufacturing. Whether transferring semiconductor wafers from one process chamber to another in a cleanroom or cutting and welding steel on the floor of an automobile manufacturing plant, robots perform many manufacturing tasks tirelessly, in hostile environments, and with high precision and repeatability. In particular, robots have found great utility in spot welding, such as in building automobile bodies from sheets of metal.
In many robotic manufacturing applications, it is cost-effective to utilize a relatively generic robot to accomplish a variety of tasks. For example, in an automotive manufacturing application, a robot may be utilized to cut, grind, or otherwise shape metal parts during one production run, and perform a variety of spot welding tasks in another. Different welding tool geometries may be advantageously mated to a particular robot to perform welding tasks at different locations or in different orientations. In these applications, a tool changer is used to mate different tools to the robot. One half of the tool changer, called the master module, is permanently affixed to a robot arm. The other half, called the tool module, is affixed to each tool that the robot may utilize. Utilities such as electrical current, air pressure, hydraulic fluid, cooling water, and the like, are fed through cables and plumbing down the robot arm, that terminate at the master module. Similar cables and plumbing carry the utilities from the tool module to the particular tool. When the tool changer halves are mated, the utilities are transferred across the changer and available at the tool.
Spot welding requires high electrical current, typically on the order of 20,000 Amperes (A). The high current is generated by a transformer that has traditionally been closely coupled to the welder, or xe2x80x9cgun,xe2x80x9d on the end of the robot arm. This arrangement is often referred to in the art as a xe2x80x9ctransgun.xe2x80x9d Primary power, in the range of 200 A at 460 Volts (V), is typically supplied by cable along the robot arm, and is coupled through a tool changer to the transgun. Secondary power, in the range of 20,000 A at 24 V, is supplied from the transformer to the welding guns by independent, short cables known as xe2x80x9cshunt cables.xe2x80x9d A tool changer for such a system, including the high-power coupling, is described in U.S. Pat. No. 6,116,966, issued Sep. 12, 2000 to Little, et al., entitled xe2x80x9cHigh-Power Electrical Contacts for Robotic Tool Changer,xe2x80x9d and assigned to the assignee the present invention, the disclosure of which is incorporated herein in its entirety.
However, in spot welding applications requiring large guns, the weight of the tool may approach the load limit of the robot. In these applications, the welding transformer is mounted on the floor close to the robot. This configuration is referred to as a xe2x80x9cremotexe2x80x9d or xe2x80x9chip mountedxe2x80x9d gun. In hip mounted guns, the high-current secondary power must be transferred from the transformer, along the robot arm, through a tool changer, and then to the welding gun. Because the high current densities in cables carrying secondary power generate large magnetic fields when the current changes, the cables will move, or xe2x80x9ckick,xe2x80x9d as the welding gun cycles through the spot welding process. Resultaiitly, cables, called xe2x80x9ckicklessxe2x80x9d cables, have been developed to facilitate the transfer of secondary power. A typical kickless cable distributes multiple positive and negative polarity conductors within a single cable sheath, such that their respective induced magnetic fields tend to cancel each other out, resulting in a cable with significantly less overall xe2x80x9ckick.xe2x80x9d Additionally, kickless cables typically circulate water or other coolant through the interstitial spaces between conductors within the cable sheath for thermal cooling. Kickless cables are terminated with a connector that typically comprises opposite polarity plates bound together, with an insulator disposed between them. The connectors additionally contain connection points for the circulation of coolant. To span short spaces, such as from the tool changer to the welding gun, shunt cables are typically used.
The present invention comprises a robotic tool changer, having a master module and a tool module adapted to be coupled and decoupled. A first pair of electrical contacts is associated with the master module and a second pair of electrical contacts is associated with the tool module. At least one of the pair of contacts is moveable between an extended and retracted position, and is biased towards the extended position. When the master and tool modules assume a coupled relationship, the first and second pair of contacts are disposed adjacent to each other. When coupled, and when the moveable pair of contacts assumes the extended position, the first and second pairs of contacts are disposed in a spaced apart relationship. An actuator is associated with the robotic tool changer for engaging the moveable pair of contacts and moving the moveable pair of contacts to the retracted position, where the moveable pair of contacts engage the other pair of contacts and establishes an electrical connection between the first and second pairs of contacts.
According to one embodiment of the present invention, a robotic tool changer is adapted to connect directly to a kickless cable carrying a secondary current. The tool changer includes a master module and a tool module adapted to be coupled and decoupled, with a pair of contacts secured to the tool module, and a pair of contacts secured to the master module. Each of the master module contacts includes a contact surface and a connector tab. The pair of master module contacts are arranged and spaced such that the associated connector tabs cooperate to directly receive and connect to the kickless cable.
In another embodiment, the present invention comprises a system for transferring secondary current across a robotic tool changer having a master module and a tool module matable to each other. The system includes a first pair of horizontally aligned contacts slideably mounted to the master module and laterally adjustable thereon, each contact having a horizontal plate for establishing electrical contact and a vertical connector tab for attachment to an electrical cable. The system also includes a pneumatic actuator associated with the master module and selectively moveable between extended and retracted positions. Additionally, the system includes a second pair of horizontally aligned contacts, each contact having a horizontal plate for establishing electrical contact and a vertical connector tab for attachment to an electrical cable, wherein the second pair of contacts are slideably mounted to the tool module and are both laterally adjustable thereon and moveable vertically between extended and retracted positions. Finally, the system includes at least one spring disposed between the tool module and each of the second pair of contacts for biasing the second pair of contacts to the extended position, where the contacts are disposed in spaced apart relationship to the first pair of contacts when the master and tool modules are mated. When the actuator is selectively actuated, the actuator engages the second pair of contacts and moves the second pair of contacts from the extended position to the retracted position, where the second pair of contacts engages the first pair of contacts and forms an electrical connection therebetween.